Disk drive devices are information storage devices that use magnetic media to store data and a movable slider with a read/write head positioned over the magnetic media to selectively read data from and write data to the magnetic media.
FIG. 1a illustrates a typical disk drive device and shows a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a slider 103 incorporating a read/write head. A voice-coil motor (VCM, not labeled) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. In operation, a lift force is generated by the aerodynamic interaction between the slider 103 and the spinning magnetic disk 101. The lift force is opposed by equal and opposite spring forces applied by the HGA 100 such that a predetermined fly-height above the surface of the spinning disk 101 is maintained over a full radial stroke of the motor arm 104.
FIG. 1b illustrates a perspective view of the slider shown in FIG. 1a in a bottom view. As illustrated, a magnetic read/write head 116, which is used for realizing data reading/writing operation of the slider 103 relative to the disk 101, is formed on one side surface of the slider 103. The slider 103 has an air bearing surface (ABS) 117 facing to the disk 101. When the disk drive device is in operation, an aerodynamic interaction is generated between the ABS 117 of the slider 103 and the rotary disk 101 in a high speed, thus making the slider 103 floating over the disk 101 dynamically to perform data reading/writing operation.
The clearance or spacing between the slider and the disk surface, concretely between a “minfly point” of the slider and the disk surface, is called fly-height, wherein the “minfly point” of the slider is the point which most closes to the disk surface. The flying dynamics of the slider and the fly-height are influenced by factors such as the rotation speed of the disk, the aerodynamic shape of the slider's ABS, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
Disk drives have been proposed to use a fly-height actuator for changing the spacing between the slider and the disk surface. One type of fly-height actuator is a thermal actuator with an electrically-resistive heater located on the slider near the read/write head. When current is applied to the heater, the heater expands and causes the read/write head to “protrude” and thus move closer to the disk surface. Other fly-height actuators for moving the read/write head relative to the slider include electrostatic micro-actuators and piezoelectric actuators. Another type of fly-height actuator, also based on thermal, electrostatic or piezoelectric techniques, changes the head-disk spacing by altering the air-flow or the shape of the slider's ABS. The clearance between the slider and the disk can be controlled and maintained by the above-mentioned fly-height actuators.
Due to the recent trend of high capacity, high density, and compact disk drive devices, there has been a corresponding increase in bit density in a tangential direction measured in bits-per-inch (BPI) and track density in a radial direction measured in tracks-per-inch (TPI), thereby requiring more delicate operations relative to the control of the disk drive devices.
Though the clearance between the slider and the disk can be maintained by the fly-height actuator, the spacing between the read head and the disk surface can not be kept the same because the read head should not be the “minfly point” as it is too sensitive towards mechanical impact. Accordingly, even maintained in the same clearance, different sliders have different performance because of their different read head design.
Typically, to judge the slider, DFH (dynamic fly-height) gamma ratio is a critical parameter that describes the motion of the mechanical minfly point of the slider compared to the read head movement. To clarify the DFH gamma ratio, a term “Rgap spacing loss” is introduced that means the spacing between the read head and the minfly point of the slider when the slider is flying over a rotating disk. The Rgap spacing loss is sensitive to the performance of the slider, especially the read performance. The lower the numerical gamma ratio value is, the larger the gap between the minfly point and the read head is, that is to say, the larger the Rgap spacing loss is. Slider design objective is to achieve a gamma ratio as close as possible to 1. A gamma ratio of 1 would be ideal for tribology and magnetic performance because it keeps the gap between the read head and the minfly point of the slider at a constant value so as to make the spacing between the read head and the disk to be a constant value. Therefore, testing of the DFH Gamma ratio can provide some data on how to improve or optimize the slider.
In the prior art, we can easily model or measure the DFH gamma ratio using AFM (Atomic Force Microscope) or Wyko-DFH protrusion profile. However, they measure the slider in the static condition or without flying media cooling effect, so the gamma ratio measured by the conventional method can not reflect the slider in actual rotating disk case and can not provide accurate data for optimizing the slider. Another current available testing method of the DFH gamma ratio is using resolution to roughly represent the Rgap spacing. Generally, the resolution value is calculated by the following equation:RESM=TAA(MF)/TAA(LF)wherein TAA(MF) (Track Average Amplitude of Middle Frequency) is the amplitude of readback signal from the disk under the condition of middle frequency writing, while TAA(LF) (Track Average Amplitude of Low Frequency) is the amplitude of readback signal from the disk under the condition of low frequency writing. However, resolution can be affected by many factors such as reader shield gap and initial PTR (protrude) recess level. Therefore, just using resolution to estimate DFH gamma ratio is not adequate and easily mixes with other factors. The DFH gamma ratio measured by this method is also not accurate.
Hence, it is desired to provide an improved method for testing the DFH gamma ratio of the slider in actual flying case and more accurately.